Interspecific and intraspecific competition in a changing world: next-generation-sequencing and lab experiments in a cryptic species complex

Type:

Master Thesis subject (30 ECTS)

programme:

EMBC+

According to classical competition theory, interspecific competition increases with relatedness between species (Darwin, 1859), rendering coexistence of cryptic species - closely related species that are morphologically indistinguishable, but show consistent genetic differences - unlikely. Cryptic diversity is prominently present in coastal nematodes and the best studied model ‘species’ in this context is Litoditis marina, which is mostly found associated with decomposing macroalgae. Both competition and facilitation between these cryptic species have been reported in closed, homogeneous microcosms. Changing the composition of the cryptic species changes the interactions between them and abiotic factors - temperature and salinity- also have an influence on the interactions between the species. Moreover, evidence for intraspecific competition within cryptic species was found. Nevertheless, several studies have shown that cryptic species can co-occur at small geographical scales. Four of the cryptic species of Litoditis marina frequently co-occur in the littoral zone of the south-western coast and estuaries of the Netherlands. The underlying mechanisms of this co-occurrence remain unknown. Species may be able to co-occur if they show differential niches in feeding behaviour. Next-generation-sequencing can be used to determine the bacterial diets of the cryptic species to test if such a niche differentiation exist.
In this master thesis, different combinations of the species (interspecific competition) and different starting densities (intraspecific competition) will be tested to elucidate the effects and the relative importance of intra- and interspecific competition in this cryptic species complex. Response variables tested can be population growth rate and diet composition. Moreover, climate change models predict changes in salinity and temperature, so different abiotic conditions will be studied, in order to investigate possible effects of global change on the interactions and thus on the co-occurrence of the species. This thesis will consist mainly of laboratory work (setting-up experiments, molecular techniques, …).